This is a new RO1 application for a five-year study of the epidemiology of insomnia, mental disorders and substance use during adolescence. The application fits within two NIMH priority areas: 1) the principal investigator is a new investigator, and 2) the subject matter places this application under a response to PA95-014, Basic and Clinical Research on Sleep and Wakefulness. The primary purpose of the proposed study is to examine pathways from insomnia to specific mental disorders and substance use during adolescence. More specifically, we will: 1 ) estimate the increased risk of specific mental disorders and substance use attributable to insomnia among adolescents; 2) assess the occurrence of insomnia as prior, concurrent or subsequent to mental/behavioral problems and substance use, as well as chronic and episodic insomnia, by examining the natural course of insomnia; and 3) estimate the prevalence and incidence of insomnia among adolescents in an epidemiologically defined population. We propose a prospective study of a population sample of 1,000 adolescent and parent pairs, with an assessment at baseline and again after a 24-month interval. Adolescents will be 13 - 15 years old at baseline. A random sub-sample of participants (N=156) will be designated for a longitudinal sub-study with monthly assessments of sleep disturbances in order to examine the natural course of insomnia. The proposed prospective study provides a unique opportunity to extend prior research on the nature and potential sequelae of insomnia in adolescence. With this epidemiologic grounding, future examination of HPA axis dysregulation and polysomnographically determined sleep architecture could provide information on potential mechanisms of the hypothesized links between insomnia, mental disorders and substance use. Similarly, with support for the hypothesized prospective increased risk for mental disorders and substance use associated with insomnia, the proposed research may also provide grounding for an intervention trial, treating adolescent insomnia in order to reduce the risk of mental disorders and substance use.